Heretofore, it has been accepted prior art practice to provide what was generally referred to as a fast idle cam which was positioned generally in accordance with the position of the choke valve of an associated carburetor. As is well known in the art, such choke valves were and are usually positioned in accordance with engine temperature. The cam, thusly positioned, coacts with a swingable abutment operatively connected to the engine throttle valve as to thereby be effective for holding the throttle valve open a greater degree during cold engine operation while permitting the throttle valve to close to an established curb idle position, once the engine has attained some preselected operating temperature, as by permitting such swingable abutment to engage either a lowest step portion on the cam or engaging a positive non-movable abutment or stop portion formed as on the carburetor body structure. Such closing of the throttle to a curb idle position determined the absolute maximum closing of the throttle under all conditions of engine operation as well as during engine shut-down. Generally, in the past, such prior art arrangements have been found to be adequate. However, because of governmentally imposed standards relating to engine exhaust emissions, it has become necessary to provide different fuel metering characteristics to the fuel metering devices associated with such engines. This, in turn, has among other things, caused the engine to have a tendency to continue to run even after the engine ignition is turned off; such often being referred to as engine "dieseling." It has been discovered that one way of being able to terminate or avoid such "dieseling" is to further close the throttle valve beyond its normal curb idle position. However, as for reasons already described, such is not possible with the prior art arrangements.
Further, it is highly desirable to damp the rate of throttle closing movement near the end of such closing movement in order to avoid a very sudden change in the rate of air and fuel flow which, if permitted to occur, usually results in rough engine operation and, often, even stalling of the engine. The provision of such damping or dashpot means along with the requirement that the throttle valve be permitted to, at a selected time, move even further closed than the normal maximum closure of curb idle has not been attainable with prior art structures.
Accordingly, the invention as herein disclosed and claimed is primarily directed to the solution of the preceding as well as other related and attendant problems.